Photography is all relative to the creator and the viewers, so the decision of whether to underexpose, overexpose, or to expose your portraits evenly is obviously subject to personal preference. There is merit to any of the methodologies that you could apply to your own photography and it really just comes down to figuring out what works best for you and your gear.
Even then, this article isn't meant to be a debate about best practices or even which gear is best. I've just found, through the course of my own experience, that some techniques tend to work better for me and my workflow than others and I have found that others have had similar experiences.
I can tell you this: I almost always underexpose my images. I shoot with a Canon 5D Mark III and I've been using that camera for almost four years now so I feel like I have a fairly good idea what it's capabilities and limitations are. Again, let me reiterate, much of the decision to modify your exposure up or down will depend on how well you know your own gear and how you use it. One of the things that I have learned about my own raw files created by the 5D is that it is so much easier for me to recover shadow areas than it is to bring back my highlights. So if I really have to choose between my exposure settings because of a high contrast scene then I will opt to underexpose simply because my chances of evening out the exposure in postproduction will be much higher with shadow control.
I've been doing a little digging online and, this probably won't surprise you, I found some differing opinions. There are plenty of people that advocate shooting underexposed images the entire time and simply using postproduction to balance out your exposure. Yet there are others that firmly believe that you should never underexpose your shots. I found this video by Cole's Classroom to be on the one side, where he recommends to shoot underexposed images and he shows you how he brings back his shadow images.
There is also this video by Tony and Chelsea Northrup that takes an approach a little differently than what Cole's Classroom suggests. Or does it?
They urge their viewers to stop underexposing their portraits. I've watched this video several times now to make sure I didn't miss anything and I noticed a couple interesting points. In each example that Northrup uses, take a close look at his raw images before any modifications. Every single one of his raw images, straight out of the camera, was underexposed. Throughout the entire video, he tells us to stop underexposing our portraits but both portrait examples and even his wildlife example shows raw images that are in fact underexposed. With each example, he uses his Adobe Camera Raw controls to bring his exposures back up to an even range for his subject matter. So when he tells us to stop underexposing our portraits, I honestly think he's talking about the output file itself, and not necessarily the raw file.
Just for fun, I played around with a simple portrait in Lightroom after watching both these videos to try and see how much control I could take over an image that had been underexposed. So here are a few before/after sliders to give you an idea what I was looking at.
In this example, we have the original shot straight out of camera compared to the same shot where the only difference is that the exposure has been bumped up +1.5.
Now in this comparison, we're looking at the image straight out of camera compared to one where the exposure has been bumped up +1.5 and the highlights have been dropped -100.
Now just so we can compare the simple difference of using the highlights slider on the image after the exposure has been bumped up, this comparison is the difference between the two edits. The only difference is that one has had the highlights dropped in conjunction with the exposure boost.
I looked through my archives to find a shot where I had actually overexposed it, just to see if we could compare those shots against these where they had been underexposed but none of the images I had on file had any highlights that were recoverable. That's not to say that highlights can't be recovered, but in my own personal experience, it's much easier to recover, or even out, exposures that have been underexposed. In both the tutorial videos that we looked at, each of the instructors used underexposed images and then brought their exposures back up in post.
In the video by Northrup, he mentions watching your histogram several times throughout the video. That right there is probably some of the best advice that could help us know whether to underexpose or overexpose or evenly expose. He talks about clipping his whites or blacks while comparing histograms. Basically, clipping blacks or whites means that you have so much of either black or white that the entire pixel registers as a solid color (white or black), at that point those pixels are not recoverable and will stay the solid white or black that they are. Paying attention to your histogram, in camera, is your best way of determining while on the shoot, what your chances are of taking better control of your image in postproduction. If you're shooting a subject that has intense highlights and shadows to the point where you're forced to clip one or the other then that is where advanced processing techniques like exposure blending and HDR have come into play.
If you take a look at the histogram of my example shot here in Lightroom, you can see that I have a fairly decent histogram. Sure, to the eye the shot is indeed underexposed, but I've preserved all the necessary data so as to have better control over the shot in postproduction. If I were to call it done and post this shot to Instagram, then that's what Northrup is telling us to avoid. I've preserved my histogram, but that's just to set myself up for more postproduction control. Now I can make the most of that digital negative.
Technology is continually advancing, cameras are getting better and better every year, and maybe one day I'll end up owning a camera that is able to preserve highlights as well as it does the shadows. But for now, for my gear, I find that slight underexposures help me make the most of my images in postproduction.
Make sure to comment if you've found any other shoot or editing techniques that have helped you make the most out of your shots. I've found that film is still better at highlight recovery than any digital format; give me some Kodak T-Max 100 and I can preserve highlights all day long, but digital is a different beast. So if you found a better method to preserve your highlights in digital negatives then by all means let me know because I simply have not figured that one out.